System and method for delivering energy to tissue

ABSTRACT

An ablation system for treating atrial fibrillation in a patient comprises an elongate shaft having proximal and distal ends, a lumen therebetween and a housing adjacent the distal end of the elongate shaft. An energy source is coupled to the housing and is adapted to deliver energy to a target tissue so as to create a zone of ablation in the target tissue that blocks abnormal electrical activity thereby reducing or eliminating the atrial fibrillation in the patient. A sensor is adjacent the energy source and adapted to detect relative position of the energy source to the target tissue or characteristics of the target tissue. The system also has a reflecting element operably coupled with the energy source and adapted to redirect energy emitted from the energy source in a desired direction or pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 12/505,335 filed Jul. 17, 2009, which is a non-provisional of,and claims the benefit of U.S. Provisional App. No. 61/082,064 filedJul. 18, 2008, the entire contents of each are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention.

The present invention relates generally to medical devices, systems andmethods, and more specifically to improved devices, systems and methodsfor creating an ablation zone in tissue. The device may be used to treatatrial fibrillation.

The condition of atrial fibrillation (AF) is characterized by theabnormal (usually very rapid) beating of the left atrium of the heartwhich is out of synch with the normal synchronous movement (“normalsinus rhythm”) of the heart muscle. In normal sinus rhythm, theelectrical impulses originate in the sino-atrial node (“SA node”) whichresides in the right atrium. The abnormal beating of the atrial heartmuscle is known as fibrillation and is caused by electrical impulsesoriginating instead in the pulmonary veins (“PV”) [Haissaguerre, M. etal., Spontaneous Initiation of Atrial Fibrillation by Ectopic BeatsOriginating in the Pulmonary Veins, New England J Med., Vol.339:659-666].

There are pharmacological treatments for this condition with varyingdegrees of success. In addition, there are surgical interventions aimedat removing the aberrant electrical pathways from the PV to the leftatrium (“LA”) such as the Cox-Maze III Procedure [J. L. Cox et al., Thedevelopment of the Maze procedure for the treatment of atrialfibrillation, Seminars in Thoracic & Cardiovascular Surgery, 2000; 12:2-14; J. L. Cox et al., Electrophysiologic basis, surgical development,and clinical results of the maze procedure for atrial flutter and atrialfibrillation, Advances in Cardiac Surgery, 1995; 6: 1-67; and J. L. Coxet al., Modification of the maze procedure for atrial flutter and atrialfibrillation. II, Surgical technique of the maze III procedure, Journalof Thoracic & Cardiovascular Surgery, 1995; 2110:485-95]. This procedureis shown to be 99% effective [J. L. Cox, N. Ad, T. Palazzo, et al.Current status of the Maze procedure for the treatment of atrialfibrillation, Seminars in Thoracic & Cardiovascular Surgery, 2000; 12:15-19] but requires special surgical skills and is time consuming.

There has been considerable effort to copy the Cox-Maze procedure for aless invasive percutaneous catheter-based approach. Less invasivetreatments have been developed which involve use of some form of energyto ablate (or kill) the tissue surrounding the aberrant focal pointwhere the abnormal signals originate in the PV. The most commonmethodology is the use of radio-frequency (“RF”) electrical energy toheat the muscle tissue and thereby ablate it. The aberrant electricalimpulses are then prevented from traveling from the PV to the atrium(achieving conduction block within the heart tissue) and thus avoidingthe fibrillation of the atrial muscle. Other energy sources, such asmicrowave, laser, and ultrasound have been utilized to achieve theconduction block. In addition, techniques such as cryoablation,administration of ethanol, and the like have also been used.

There has been considerable effort in developing catheter based systemsfor the treatment of AF using radiofrequency (RF) energy. One suchmethod is described in U.S. Pat. No. 6,064,902 to Haissaguerre et al. Inthis approach, a catheter is made of distal and proximal electrodes atthe tip. The catheter can be bent in a J shape and positioned inside apulmonary vein. The tissue of the inner wall of the pulmonary vein (PV)is ablated in an attempt to kill the source of the aberrant heartactivity. Other RF based catheters are described in U.S. Pat. No.6,814,733 to Schwartz et al., U.S. Pat. No. 6,996,908 to Maguire et al.,U.S. Pat. No. 6,955,173 to Lesh, and U.S. Pat. No. 6,949,097 to Stewartet al.

Another source used in ablation is microwave energy. One such device isdescribed by Dr. Mark Levinson [(Endocardial Microwave Ablation: A NewSurgical Approach for Atrial Fibrillation; The Heart Surgery Forum,2006] and Maessen et al. [Beating heart surgical treatment of atrialfibrillation with microwave ablation. Ann Thorac Surg 74: 1160-8, 2002].This intraoperative device consists of a probe with a malleable antennawhich has the ability to ablate the atrial tissue. Other microwave basedcatheters are described in U.S. Pat. No. 4,641,649 to Walinsky; U.S.Pat. No. 5,246,438 to Langberg; U.S. Pat. No. 5,405,346 to Grundy etal.; and U.S. Pat. No. 5,314,466 to Stem et al.

Another catheter based method utilizes the cryogenic technique where thetissue of the atrium is frozen below a temperature of −60 degrees C.This results in killing of the tissue in the vicinity of the PV therebyeliminating the pathway for the aberrant signals causing the AF [A. M.Gillinov, E. H. Blackstone and P. M. McCarthy, Atrial fibrillation:current surgical options and their assessment, Annals of ThoracicSurgery 2002; 74:2210-7]. Cryo-based techniques have been a part of thepartial Maze procedures [Sueda T., Nagata H., Orihashi K. et al.,Efficacy of a simple left atrial procedure for chronic atrialfibrillation in mitral valve operations, Ann Thorac Surg 1997;63:1070-1075; and Sueda T., Nagata H., Shikata H. et al.; Simple leftatrial procedure for chronic atrial fibrillation associated with mitralvalve disease, Ann Thorac Surg 1996; 62: 1796-1800]. More recently, Dr.Cox and his group [Nathan H., Eliakim M., The junction between the leftatrium and the pulmonary veins, An anatomic study of human hearts,Circulation 1966; 34:412-422, and Cox J. L., Schuessler R. B., BoineauJ. P., The development of the Maze procedure for the treatment of atrialfibrillation, Semin Thorac Cardiovasc Surg 2000; 12:2-14] have usedcryoprobes (cryo-Maze) to duplicate the essentials of the Cox-Maze IIIprocedure. Other cryo-based devices are described in U.S. Pat. Nos.6,929,639 and 6,666,858 to Lafintaine and U.S. Pat. No. 6,161,543 to Coxet al.

More recent approaches for the AF treatment involve the use ofultrasound energy. The target tissue of the region surrounding thepulmonary vein is heated with ultrasound energy emitted by one or moreultrasound transducers. One such approach is described by Lesh et al. inU.S. Pat. No. 6,502,576. Here the catheter distal tip portion isequipped with a balloon which contains an ultrasound element. Theballoon serves as an anchoring means to secure the tip of the catheterin the pulmonary vein. The balloon portion of the catheter is positionedin the selected pulmonary vein and the balloon is inflated with a fluidwhich is transparent to ultrasound energy. The transducer emits theultrasound energy which travels to the target tissue in or near thepulmonary vein and ablates it. The intended therapy is to destroy theelectrical conduction path around a pulmonary vein and thereby restorethe normal sinus rhythm. The therapy involves the creation of amultiplicity of lesions around individual pulmonary veins as required.The inventors describe various configurations for the energy emitter andthe anchoring mechanisms.

Yet another catheter device using ultrasound energy is described byGentry et al. [Integrated Catheter for 3-D Intracardiac Echocardiographyand Ultrasound Ablation, IEEE Transactions on Ultrasonics,Ferroelectrics, and Frequency Control, Vol. 51, No. 7, pp 799-807]. Herethe catheter tip is made of an array of ultrasound elements in a gridpattern for the purpose of creating a three dimensional image of thetarget tissue. An ablating ultrasound transducer is provided which is inthe shape of a ring which encircles the imaging grid. The ablatingtransducer emits a ring of ultrasound energy at 10 MHz frequency. In aseparate publication [Medical Device Link, Medical Device and DiagnosticIndustry, February 2006], in the description of the device, the authorsassert that the pulmonary veins can be imaged.

While these devices and methods are promising, improved devices andmethods for creating a heated zone of tissue, such as an ablation zoneare needed. Furthermore, it would also be desirable if such devicescould create single or multiple ablation zones to block abnormalelectrical activity in the heart in order to lessen or prevent atrialfibrillation. It would also be desirable if such devices could be usedin the presence of blood or other body tissues without coagulating orclogging up the ultrasound transducer. Such devices and methods shouldbe easy to use, minimally invasive, cost effective and simple tomanufacture.

2. Description of the Background Art.

Other devices based on ultrasound energy to create circumferentiallesions are described in U.S. Pat. Nos. 6,997,925; 6,966,908; 6,964,660;6,954,977; 6,953,460; 6,652,515; 6,547,788; and 6,514,249 to Maguire etal.; U.S. Pat. Nos. 6,955,173; 6,052,576; 6,305,378; 6,164,283; and6,012,457 to Lesh; U.S. Pat. Nos. 6,872,205; 6,416,511; 6,254,599;6,245,064; and 6,024,740; to Lesh et al.; U.S. Pat. Nos. 6,383,151;6,117,101; and WO 99/02096 to Diederich et al.; U.S. Pat. No. 6,635,054to Fjield et al.; U.S. Pat. No. 6,780,183 to Jimenez et al.; U.S. Pat.No. 6,605,084 to Acker et al.; U.S. Pat. No. 5,295,484 to Marcus et al.;and WO 2005/117734 to Wong et al.

BRIEF SUMMARY OF THE INVENTION

The present invention relates generally to medical devices and methods,and more specifically to medical devices and methods used to deliverenergy to tissue as a treatment for atrial fibrillation and othermedical conditions.

In a first aspect of the present invention, an ablation system fortreating atrial fibrillation in a patient comprises an elongate shafthaving a proximal end, a distal end, and lumens therebetween. A housingis adjacent the distal end of the elongate shaft and an energy source iscoupled to the housing. The energy source is adapted to deliver energyto a target tissue so as to create a zone of ablation in the targettissue that blocks abnormal electrical activity thereby reducing oreliminating the atrial fibrillation in the patient. The system also hasa reflecting element operably coupled with the energy source and adaptedto redirect energy emitted from the energy source in a desired directionor pattern.

The housing may be rotatable about its longitudinal axis and the energymay be redirected by the reflecting element in a generally circularpattern. The energy source may be recessed from a distal end of thehousing such that the energy source does not contact the target tissuein operation.

The energy source may comprise an ultrasound transducer that is adaptedto emit a beam of ultrasound energy. The beam may have a frequency inthe range of 5 to 20 MHz and a generator may be electrically coupledwith the ultrasound transducer. The generator may provide an excitationvoltage of 5 to 300 volts peak-to-peak to the ultrasound transducer. Theexcitation voltage may have a duty cycle ranging from 0% to 100%, andmay have a repetition frequency of about 40 KHz. The energy source maybe adapted to deliver one of radiofrequency energy, microwaves, photonicenergy, thermal energy, and cryogenic energy. The energy source maycomprise a flat face, a concave face or a convex face. The face may beadapted to act as a lens for focusing the energy delivered by the energysource.

The system may comprise a sensor adjacent the energy source and that isadapted to detect relative position of the energy source to the targettissue or characteristics of the target tissue. The sensor may beadapted to detect a gap between a surface of the target tissue and theenergy source. The sensor may be adapted to determine characteristics ofthe target tissue such as tissue thickness or ablation zone depth. Thesensor may comprise an ultrasound transducer. The energy source maycomprise the same ultrasound transducer as the sensor. Other sensors maycomprise an infrared sensor or strain gage.

The reflecting element may be non-expandable. It may redirect the energyin a collimated beam through a portion of the housing or it may redirectthe energy in a focused beam that converges toward a focal point or afocal ring, or it may alter the focus of the beam to provide a moreuniformly collimated beam. The reflecting element may comprise an angledouter surface that is adapted to redirect the energy. The angle of theouter surface may range from 30 to 60 degrees relative to a longitudinalaxis of the housing. The angled face may comprise a flat surface. Thereflecting element may comprise a curved outer surface that redirectsthe energy. The reflecting element may redirect the energy through asidewall of the housing. The reflecting element may be movable relativeto the energy source so that the energy exits the housing at varyingangles or so that the energy is reflected outward away from the housingin a circular pattern. The reflecting element may be adapted to redirectthe energy from the energy source to form a ring shaped beam of energy.The reflecting element may comprise a liquid-gas interface or abowl-shaped reflector that is centered around a longitudinal axis of thehousing. The liquid-gas interface may comprise a plurality of expandablereflectors positioned adjacent one another. The reflecting element maycomprise two reflecting portions each having a different shape or anglerelative to the energy source so that the energy is redirected in two ormore directions or patterns. The energy may be redirected in a firstpattern comprising a collimated beam and the energy may be redirected ina second pattern comprising a focused beam.

The system may further comprise a processor that is adapted to controlthe energy provided by the energy source based on information receivedfrom the sensor. The system may have a lens adjacent the energy sourceand that is adapted to adjust beam pattern of the energy emitted fromthe energy source.

The target tissue may comprise left atrial tissue, a pulmonary vein ortissue adjacent thereto. The zone of ablation may comprise a linearablation path or an arcuate ablation path. The zone of ablation maycomprise a transmural ablation zone.

In another aspect of the present invention, a method for treating atrialfibrillation by ablating tissue in a patient comprises providing anablation system comprising an elongate shaft having a distal tipassembly. The distal tip assembly comprises an energy source and areflecting element. The distal tip assembly is advanced adjacent thetissue and energy is delivered from the energy source to the tissue.Energy from the energy source is reflected off of the reflecting elementso as to redirect the energy emitted from the energy source in a desireddirection or pattern. A partial or complete zone of ablation is createdin the tissue, thereby blocking abnormal electrical activity andreducing or eliminating the atrial fibrillation.

The step of advancing the distal tip assembly may comprise passing thedistal tip through an atrial septal wall. The energy source may comprisean ultrasound transducer and the step of delivering the energy maycomprise delivering a beam of ultrasound. The beam may comprise afrequency in the range of 5 to 20 MHz. Delivering the energy maycomprise providing an excitation voltage ranging from 5 to 300 voltspeak-to-peak to the ultrasound transducer. Delivering energy maycomprise delivering one of radiofrequency energy, microwaves, photonicenergy, thermal energy and cryogenic energy.

The step of reflecting the energy may comprise redirecting the energy ina collimated beam of energy or focusing the energy so that it convergestoward a focal point or a focal ring. Reflecting the energy may compriseredirecting the energy so that it exits a sidewall of the housing. Thereflecting element may be non-expandable or it may comprise anexpandable member such as a balloon or collapsible nested reflectors(e.g. similar to a collapsible parabolic dish used in satellitecommunications), and the step of reflecting the energy may compriseexpanding the expandable member. Reflecting the energy may comprisemoving the reflecting element relative to the housing such as byrotating it. The reflecting element may comprise a first reflectingportion and a second reflecting portion. The energy reflected off thefirst portion may be redirected in a first direction, and the energyreflected off the second portion may be redirected in a second directiondifferent than the first direction.

The zone of ablation may comprise a linear or arcuate zone of ablation.The step of creating the zone of ablation may comprise encircling thezone of ablation around a pulmonary vein or left atrial tissue. The zoneof ablation may comprise a transmural lesion.

The method may further comprise cooling the energy source with a coolingfluid. The system may further comprise a sensor that is adapted to senserelative position of the energy source to the target tissue orcharacteristics of the target tissue. The ablation system may furthercomprise a processor, and the method may further comprise controllingenergy delivery based on information from the sensor.

The method may comprise sensing a gap distance between the energy sourceand a surface of the tissue with the sensor. The method may also includesensing characteristics of the tissue such as tissue thickness or depthof the ablation zone, with the sensor. The sensor may comprise anultrasound sensor and the energy source may also comprise the sameultrasound transducer. The method may include switching modes betweendelivering energy with the ultrasound transducer and sensing tissuecharacteristics with the ultrasound transducer sensor.

These and other embodiments are described in further detail in thefollowing description related to the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are drawings of the system of the preferred embodiments ofthe invention;

FIGS. 3A-3B illustrate the reflecting surface of the system and energybeam of the preferred embodiments of the invention; and

FIG. 4-5 are drawings of the energy beam and the zone of ablation of thepreferred embodiment of the invention.

FIG. 6 illustrates an embodiment of the system.

FIG. 7 illustrates the energy source having a backing.

FIGS 8A-8B illustrate other embodiments of the energy source.

DETAILED DESCRIPTION OF THE INVENTION

The following description of preferred embodiments of the invention isnot intended to limit the invention to these embodiments, but rather toenable any person skilled in the art to make and use this invention.

As shown in FIG. 1, the energy delivery system 10 of the preferredembodiments includes an energy source 12 that functions to provide asource of ablation energy; a reflecting surface 100 that functions toredirect the ablation energy from the energy source 12; a sensor; and aprocessor (not shown), coupled to the sensor and to the energy source12, which may controls the energy source 12 based on the informationfrom the sensor. The energy delivery system 10 is preferably designedfor delivering energy to tissue, more specifically, for deliveringablation energy to tissue, such as heart tissue, to create a conductionblock—isolation and/or block of conduction pathways of abnormalelectrical activity, which typically originate from the pulmonary veinsin the left atrium—for treatment of atrial fibrillation in a patient.The system 10, however, may be alternatively used with any suitabletissue in any suitable environment and for any suitable reason.

The Energy Source. As shown in FIG. 1, the energy source 12 of thepreferred embodiments functions to provide a source of ablation energy.The ablation energy is preferably in the form of an energy beam 20emitted from the energy source 12. The energy source 12 is preferably anultrasound transducer that emits an ultrasound beam, but mayalternatively be any suitable energy source that functions to provide asource of ablation energy. Some suitable sources of ablation energy mayinclude radio frequency (RF) energy, microwaves, photonic energy, andthermal energy. The therapy could alternatively be achieved using cooledfluids (e.g., cryogenic fluid). The energy delivery system 10 preferablyincludes a single energy source 12, but may alternatively include anysuitable number of energy sources 12. For example, the system 10 mayinclude multiple energy sources configured in a ring, such that incombination they emit an annular shaped energy beam 20.

The energy source 12 is preferably an ultrasound transducer that ispreferably made of a piezoelectric material such as PZT (lead zirconatetitanate) or PVDF (polyvinylidine difluoride), or any other suitableultrasound beam emitting material. The transducer may further includecoating layers such as a thin layer of a metal. Some suitable transducercoating metals may include gold, stainless steel, nickel-cadmium,silver, plastic, metal-filled graphite, a metal alloy, and any othersuitable material that functions to increase the efficiency of couplingof the energy beam 20 into the surrounding fluid 28 or performs anyother suitable functions. The transducer is preferably a cylindricaltransducer, as shown in FIGS. 3A and 3B, such that it preferably emitsenergy beam 20 from the outer face of the cylinder (e.g. radially outfrom the face of the energy source). The energy beam 20 is preferablyemitted radially 360 degrees around the energy source 12, but mayalternatively be emitted from any suitable portions) of the energysource. The transducer may alternatively be a generally flat transducer,such as a disc, as shown in FIGS. 1 and 2. The disc transducerpreferably emits energy beam 20 from at least one of the faces of thedisc. The faces of the disc that emit the energy beam 20 are preferablyflat, but may alternatively be either concave or convex to achieve aneffect of a lens. The disc transducer preferably has a circulargeometry, but may alternatively be elliptical, polygonal, doughnutshaped, or any other suitable shape.

As shown in FIG. 1, the energy source 12 of the preferred embodiments ispreferably coupled to at least one electrical attachment 14. Theelectrical attachment 14 of the preferred embodiments functions toenergize the energy source 12 such that it emits an energy beam 20. Theenergy delivery system 10 preferably includes two electrical attachments14 and 14′, but may alternatively include any suitable number ofelectrical attachments to energize the energy source 12. The energydelivery system 10 of the preferred embodiments also includes anelectrical generator (not shown) that functions to provide power to theenergy source 12 via the electrical attachment(s) 14. When energized bythe generator the energy source 12 emits an energy beam 20. Thegenerator provides the appropriate frequency and voltage to the energysource 12 to create the desired energy beam 20. In the case of anultrasound energy source 12, the ultrasound frequency is preferably inthe range of 1 to 25 MHz and more preferably in the range of 5 to 20MHz. The energy of the energy beam 20 is determined by the excitationvoltage applied to the energy source 12. The voltage is preferably inthe range of 5 to 300 volts peak-to-peak. In addition, a variable dutycycle is preferably used to control the average power delivered to theenergy source 12. The duty cycle preferably ranges from 0% to 100%, witha repetition frequency of approximately 40 kHz, which is preferablyfaster than the time constant of thermal conduction in the tissue.

When energized with an electrical pulse or pulse train by the electricalattachment 14 and/or 14′, the energy source 12 emits an energy beam 20(such as a sound wave). The properties of the energy beam 20 aredetermined by the characteristics of the energy source 12, the matchinglayer, the backing (described below), and the electrical pulse fromelectrical attachment 14. These elements determine the frequency,bandwidth, and amplitude of the energy beam 20 (such as a sound wave)propagated into the tissue. As shown in FIG. 4, the energy source 12emits energy beam 20 such that it interacts with tissue 276 and forms alesion (zone of ablation 278). The energy beam 20 is preferably anultrasound beam. The tissue 276 is preferably presented to the energybeam 20 within the collimated length L. The front surface 280 of thetissue 276 is at a distance d (282) away from the face of a housing 16.As the energy beam 20 travels through the tissue 276, its energy isabsorbed by the tissue 276 and converted to thermal energy. This thermalenergy heats the tissue to temperatures higher than the surroundingtissue resulting in a heated zone 278. In the zone 278 where the tissueis heated, the tissue cells are preferably rendered dead due to heat.The temperatures of the tissue are preferably above the temperaturewhere cell death occurs in the heated zone 278 and therefore, the tissueis said to be ablated. Hence, the zone 278 is preferably referenced asthe ablation zone or lesion.

The shape of the lesion or ablation zone 278 formed by the energy beam20 depends on the characteristics of suitable combination factors suchas the energy beam 20, the energy source 12 (including the material, thegeometry, the portions of the energy source 12 that are energized and/ornot energized, etc.), the matching layer, the backing, the electricalpulse from electrical attachment 14 (including the frequency, thevoltage, the duty cycle, the length of the pulse, etc.), and thecharacteristics of target tissue that the beam 20 contacts and thelength of contact or dwell time. These characteristics can be changedbased on the information detected by the sensor (as described below),thereby changing the physical characteristics of the lesion.

The housing 16 also functions to provide a barrier between the face ofthe energy source 12 and blood or tissue. When fluid flow isincorporated, the fluid may flow past the energy source therebypreventing blood from coagulating thereon. In preferred embodiments, thecoolant flows past the energy source at approximately 1 ml/minute, butmay be increased or decreased as desired. Additionally, since the energysource is disposed in the housing, the energy source will not directlycontact tissue, thereby also preventing coagulation on the energysource.

Additional details on the energy source, energy source configurations,the housing and adjacent components are disclosed in US20090312693A1,U.S. patent application Ser. No. 12/480,256 and US20090312673A1, U.S.patent application Ser. No. 12/482,640 , the entire contents of whichare incorporated herein by reference.

The energy source 12 is preferably one of several variations. In a firstvariation, as shown in FIG. 7, the energy source 12 is a disc with aflat front surface. In a second variation, as shown in FIGS. 8A and 8B,the energy source 12′ includes an inactive portion 42. In thisvariation, the inactive portion 42 does not emit an energy beam when theenergy source 12 is energized, or may alternatively emit an energy beamwith a very low (substantially zero) energy. The inactive portion 42preferably functions to aid in the temperature regulation of the energysource, i.e. preventing the energy source from becoming too hot. In afull disk transducer, as shown in FIG. 7, the center portion of thetransducer generally becomes the hottest portion of the transducer whileenergized. By removing the center portion or a portion of the centerportion of the transducer, the energy emitted from the transducer ispreferably distributed differently across the transducer, and the heatof the transducer is preferably more easily dissipated.

The inactive portion 42 is preferably a hole or gap defined by theenergy source 12′. In this variation, a coolant source may be coupledto, or in the case of a coolant fluid, it may flow through the hole orgap defined by the energy source 12′ to further cool and regulate thetemperature of the energy source 12′. The inactive portion 42 mayalternatively be made of a material with different material propertiesfrom that of the energy source 12′. For example, the material ispreferably a metal, such as copper, which functions to draw or conductheat away from the energy source 12. Alternatively, the inactive portionis made from the same material as the energy source 12, but with theelectrode plating removed or disconnected from the electricalattachments 14 and or the generator. The inactive portion 42 ispreferably disposed along the full thickness of the energy source 12′,but may alternatively be a layer of material on or within the energysource 12′ that has a thickness less than the full thickness of theenergy source 12′. As shown in FIG. 8A, the energy source 12′ ispreferably a doughnut-shaped transducer. As shown, the transducerpreferably defines a hole (or inactive portion 42) in the center portionof the transducer. The energy source 12′ of this variation preferablyhas a circular geometry, but may alternatively be elliptical, polygonal(FIG. 8B), or any other suitable shape. The energy source 12′ preferablyincludes a singular, circular inactive portion 42, but may alternativelyinclude any suitable number of inactive portions 42 of any suitablegeometry, as shown in FIG. 8B. The total energy emitted from the energysource 12 is related to the surface area of the energy source 12 that isactive (ke. emits energy beam 20). Therefore, the size and location ofinactive portions 42 preferably reduce heat build-up in the energysource 12, while allowing the energy source 12 to provide as much outputenergy as possible or as desired.

As shown in FIGS. 6 and 7, the energy delivery system 10 of thepreferred embodiments also includes a backing 22, coupled to the energysource 12. The energy source 12 is preferably bonded to the end of abacking 22 by means of an adhesive ring 24. Backing 22 is preferablymade of a metal or a plastic, such that it provides a heat sink for theenergy source 12. The attachment of the energy source 12 to the backing22 is such that there is a pocket 26 between the back surface of theenergy source 12 and the backing 22. This pocket preferably contains amaterial with acoustic impedance significantly different than thematerial of the energy source 12, and preferably creates an acousticallyreflective surface. Most of the ultrasound that would otherwise exitfrom the back of the energy source 12 is preferably redirected back intothe energy source 12 from the pocket, and out through the front surfaceof the energy source 12. Additionally, the material in the pocket isalso preferably a good thermal conductor, so that heat can be removedfrom the energy source, and electrically conductive such that it mayconnect the electrical wires to the rear surface of the energy source.The pocket is preferably one of several variations. In a first version,the backing 22 couples to the energy source at multiple points. Forexample, the backing preferably includes three posts that preferablycouple to the outer portion such that the majority of the energy source12 is not touching a portion of the backing. In this variation, a fluidor gel preferably flows past the energy source 12, bathing preferablyboth the front and back surfaces of the energy source 12. In a secondvariation, the pocket is an air pocket 26 between the back surface ofthe energy source 12 and the backing 22. The air pocket 26 functionssuch that when the energy source 12 is energized by the application ofelectrical energy, the emitted energy beam 20 is reflected by the airpocket 26 and directed outwards from the energy source 12. The backing22 preferably defines an air pocket of a cylindrical shape, and morepreferably defines an air pocket 26 that has an annular shape. Thebacking defines an annular air pocket by further including a center postsuch that the backing is substantially tripod shaped when viewed incross section, wherein the backing is coupled to the energy source 12towards both the outer portion of the energy source and towards thecenter portion of the energy source. The air pocket 26 may alternativelybe replaced by any other suitable material such that a substantialportion of the energy beam 20 is directed outwards from the energysource 12.

While the energy source 12 is emitting an energy beam 20, the energysource may become heated. The energy source 12 is preferably maintainedwithin a safe operating temperature range by cooling the energy source12. Cooling of the energy source 12 is preferably accomplished bycontacting the energy source 12 with a fluid, for example, saline or anyother physiologically compatible fluid, preferably having a lowertemperature relative to the temperature of the energy source 12. In afirst version, the temperature of the fluid is preferably cold enoughthat it both cools the transducer and the target tissue. In thisversion, the temperature of the fluid or gel is preferably between −5and 5 degrees Celsius and more preferably substantially equal to zerodegrees Celsius. In a second version, the temperature of the fluid iswithin a temperature range such that the fluid cools the energy source12, but it does not cool the target tissue however, and may actuallywarm the target tissue. The fluid may alternatively be any suitabletemperature to sufficiently cool the energy source 12. By way of anexample, as shown in FIG. 7, the backing 22 preferably has a series ofgrooves 36 disposed longitudinally along the outside wall that functionto provide for the flow of a cooling fluid 2S substantially along theouter surface of backing 22 and past the face of the energy source 12.The series of grooves may alternatively be disposed along the backing inany other suitable configuration, such as helical. The resulting fluidflow lines are depicted as 30 in FIG. 6. The flow of the cooling fluidis achieved through a lumen 32. The fluid used for cooling thetransducer preferably exits the housing 16 through the end of thehousing 16 or through one or more apertures. The apertures arepreferably a grating, screen, holes, drip holes, weeping structure orany of a number of suitable apertures. The fluid preferably exits thehousing 16 to contact the target tissue and to cool the tissue.

The Reflecting Surface. As shown in FIG. 1, the reflector 100 of thepreferred embodiments functions to redirect the energy beam 20 from theenergy source 12. The reflecting surface 100 preferably redirects theenergy beam 20 from the energy source 12 out of housing 16 andpreferably towards the target tissue. The reflecting surface 100preferably redirects the energy beam 20 such that it is a collimatedbeam exiting the housing 16 (as shown in FIGS. 2 and 3), the reflectingsurface 22 may alternatively redirect the energy beam 20 such that it isa focused beam that preferably converges towards a substantially singlefocal point or towards focal point ring. The reflecting surface ispreferably one of several variations. In a first variation, as shown inFIG. 1, the reflecting surface 100 is an angled reflector device. Thereflector device is preferably a cylindrical reflector with a face ofthe reflector at an angle to the longitudinal axis of the housing 16.The energy source 12 is preferably positioned towards the distal end ofthe housing 16 with the front face pointing towards the reflectordevice, which is preferably positioned along the same axis (thelongitudinal axis of the housing 16) as the energy source 12. The energybeam 20 from the energy source 12 is preferably redirected from thereflecting surface such that it exits the housing 16 through a sideportion of the housing. The reflector device is preferably made from amaterial that reflects the energy beam 20, such as metal, but mayalternatively be a gas filled reflector device such as a gas filledballoon. The angled face of the reflector is preferably flat, but mayalternatively be a non-planar face, such as a curved, convex or concavesurface. The angle of the reflector preferably ranges betweensubstantially 0 degrees, more preferably substantially 30-60 degrees,and most preferably substantially 45 degrees. The reflector device ispreferably set at a fixed angle with respect to the energy source 12,but may alternatively be movable, such as rotated or pivoted, to alterthe angle that the energy beam 20 will exit the housing 16. Referring toFIG. 1, the reflector device is preferably secured to the housing 16 bymeans of a distal adhesive band 1418, but may alternatively be coupledto the housing 16 with any other suitable chemical and/or mechanicalconnection such as adhesive, welding, pins and/or screws. The adhesiveband 1418 preferably includes a passageway 1445 for the flow of acooling fluid (as described below).

In the first variation of the reflecting surface 100, the energy beam 20exiting from the housing 16 is preferably directed along an ablationpath such that it propagates into tissue. As the energy beam 20propagates into the tissue along the ablation path, it preferablyprovides a partial or complete zone of ablation along the ablation path.The zone of ablation along the ablation path preferably has any suitablegeometry to provide therapy, such as providing a conduction block fortreatment of atrial fibrillation in a patient. The zone of ablationalong the ablation path may alternatively provide any other suitabletherapy for a patient. A linear ablation path is preferably created bymoving the system 10, and the energy source 12 within it, in an X, Y,and/or Z direction. A generally circular or elliptical ablation path ispreferably created by rotating the energy source 12 about an axis. In afirst version, the reflecting surface 100 is preferably rotated withinthe housing 16 and about the longitudinal axis of the housing 16, suchthat as the energy source 12 is energized and emitting the energy beam20, the beam will be reflected out of the housing in 360 degrees. Theenergy beam 20 that is redirected by the reflecting surface 100preferably exits a side portion of the housing though a window locatedaround the circumference of the distal tip assembly 16. The window ispreferably made of a material that is transparent to ultrasound wavessuch as a poly 4-methyl, 1-pentene (PMP) material or may alternativelybe an open window. In a second version, the entire system 10 willrotate, rotating the energy beam 20 that exits from at least one singleportion of the housing 16. The system 10 is preferably rotated about thelongitudinal axis of the housing 16, but may alternatively be rotatedabout an axis off set from the longitudinal axis of the housing 16. Inthis version, the energy beam 20 preferably sweeps a generally circularpath.

In a second variation, as shown in FIG. 2, the reflecting surface 100 isalso an angled reflector device. The reflector device is preferably asubstantially flat reflecting device, with an inside face of thereflector at an angle to the front face of the energy source 12. Theenergy source 12 is preferably positioned adjacent to a side wall of thehousing 16 with the front face the energy source 12 pointing towards thereflector device. The energy beam 20 from the energy source 12 ispreferably redirected from the reflecting surface such that it exits thehousing 16 through an end portion of the housing. The energy beam 20that is redirected by the reflecting surface 100 preferably exits theend portion of the housing though a window. The window is preferably anopen window, but may alternatively be made of a material that istransparent to ultrasound waves such as a poly 4-methyl, 1-pentene (PMP)material. The reflector device is preferably made from a material thatreflects the energy beam 20, such as metal, but may alternatively be agas filled reflector device such as a gas filled balloon. The angledface of the reflector is preferably flat, but may alternatively be anonplanar face, such as a curved, convex or concave surface. The angleof the reflector preferably ranges between substantially 0-90 degrees,more preferably substantially 30-60 degrees, and most preferablysubstantially 45 degrees. The reflector device is preferably set at afixed angle with respect to the energy source 12, but may alternativelybe movable, such as rotated or pivoted, to alter the angle that theenergy beam 20 will exit the housing 16. The reflecting surface 22preferably includes a passageway 1445 for the flow 28 of a cooling fluid(as described below).

In the second variation of the reflecting surface 100, the energy beam20 exiting from the housing 16 is preferably directed along an ablationpath such that it propagates into tissue. As the energy beam 20propagates into the tissue along the ablation path, it preferablyprovides a partial or complete zone of ablation along the ablation path.A linear ablation path is preferably created by moving the system 10,and the energy source 12 within it, in an X, Y, and/or Z direction.Alternatively, a generally circular or elliptical ablation path ispreferably created by rotating the housing 16 about an axis. In a firstversion, the housing 16 is preferably rotated about its longitudinalaxis. Because the energy beam 20 is redirected by the reflecting surface100, as shown in FIG. 2, the energy beam 20 exits the housing at adistance from the longitudinal axis of the housing. Therefore, as thehousing 16 is moved in a circular or elliptical path, the energy beam 20will contact the tissue, creating a corresponding generally circular orelliptical ablation path.

In a third variation, as shown in FIGS. 3A and 3B, the reflectingsurface 100 is also an angled, bowl-shaped reflector device centeredaround the longitudinal axis of the housing 16. The inside surface ofthe reflector device is preferably a substantially linear surface (incross section, as shown in FIG. 3B) at an angle to the front face of theenergy source 12. The angled face of the reflector is preferably flat,but may alternatively be a non-planar face, such as a curved, convex orconcave surface, or combinations thereof. The energy source 12 ispreferably a cylindrical energy source 12, positioned along thelongitudinal axis of the housing 16. The energy beam 20 from the energysource 12 preferably exits the energy source radially and is preferablyredirected from the reflecting surface such that it exits the housing 16as a ring shaped energy beam (as shown in FIG. 3A) through an endportion of the housing. The energy beam 20 that is redirected by thereflecting surface 100 preferably exits the end portion of the housingthough a window. The window is preferably an open window, but mayalternatively be made of a material that is transparent to ultrasoundwaves such as a poly 4-methyl, 1-pentene (PMP) material. The reflectordevice is preferably made from a material that reflects the energy beam20, such as metal, but may alternatively be a gas filled reflectordevice such as a gas filled balloon. The angle of the reflectorpreferably ranges between substantially 0-90 degrees, more preferablysubstantially 30-60 degrees, and most preferably substantially 45degrees. The reflector device is preferably set at a fixed angle withrespect to the energy source 12, but may alternatively be movable, suchas rotated or pivoted, to alter the angle that the energy beam 20 willexit the housing 16.

In the third variation of the reflector 100, the energy beam 20 exitingfrom the housing 16 is preferably ring-shaped, as shown in FIG. 3A, andtherefore preferably creates a ring shaped ablation path when itinteracts with tissue and preferably provides a partial or complete zoneof ablation along the ablation path. A linear ablation path isalternatively created by the energy source 12 emitting energy beam 20from only a partial radial portion of the energy source and/or by movingthe system 10, and the energy source 12 within it, in an X, Y, and/or Zdirection. Alternatively, the energy source of the third variationreflecting surface 100 may be a flat energy source (rather than acylindrical one) with the front face towards a portion of the reflectingsurface. To create an ablation path, the energy source 12 is preferablyrotated about the longitudinal axis of the housing such that the energybeam 20 will be redirected by various portions of the reflectingsurface, creating a circular ablation path.

The Sensor. As shown in FIG. 5, the energy delivery system 10 of thepreferred embodiments also includes a sensor that functions to detectthe gap (e.g., the distance of the tissue surface from the energy source12), the thickness of the tissue targeted for ablation, and thecharacteristics of the ablated tissue. The sensor is preferably anultrasound transducer, but may alternatively be any suitable sensor,such as a strain gage, feeler gage, or IR sensor, to detect informationwith respect to the gap, the thickness of the tissue targeted forablation, the characteristics of the ablated tissue, the location ofelements of the system 10, and/or any other suitable parameter orcharacteristic.

The sensor is preferably the same transducer as the transducer of theenergy source 12 operating in a different mode (such as A-mode, definedbelow), but may alternatively be a separate ultrasound transducer or anadditional sensor 40′ as shown in FIG. 3A coupled to a top portion ofthe cylindrical energy source 12. The system 10 may include multiplesensors such as a first sensor to detect information with respect to thetarget tissue, and a second sensor to detect information with respect tothe location of the elements of the system 10. By detecting informationon the gap, the thickness of the tissue targeted for ablation, thecharacteristics of the ablated tissue, and/or the locations of theelements of the system 10, the sensor preferably functions to guide thetherapy provided by the ablation of the tissue.

In the variations of the system 10 wherein the sensor is the sametransducer as the transducer of the energy source 12 operating in adifferent mode (such as A-mode), the sensor preferably utilizes a pulseof ultrasound of short duration, which is generally not sufficient forheating of the tissue. This is a simple ultrasound imaging technique,referred to in the art as A Mode, or Amplitude Mode imaging. As shown inFIG. 5, sensor 40 preferably sends a pulse 290 of ultrasound towards thetissue 276. A portion of the beam is reflected and backscattered as 292from the front surface 280 of the tissue 276. This reflected beam 292 isdetected by the sensor 40 a short time later and converted to anelectrical signal, which is sent to the electrical receiver (not shown).The reflected beam 292 is delayed by the amount of time it takes for thesound to travel from the sensor 40 to the front boundary 280 of thetissue 276 and back to the sensor 40. This travel time represents adelay in receiving the electrical signal from the sensor 40. Based onthe speed of sound in the intervening media (fluid 286 and blood 284),the gap distance d (282) is determined. As the sound beam travelsfurther into the tissue 276, a portion 293 of it is scattered from thelesion 278 being formed and travels towards the sensor 40. Again, thesensor 40 converts this sound energy into electrical signals and aprocessor (described below) converts this information intocharacteristics of the lesion formation such as thickness, etc. As thesound beam travels still further into the tissue 276, a portion 294 ofit is reflected from the back surface 298 and travels towards thetransducer. Again, the sensor 40 converts this sound energy intoelectrical signals and the processor converts this information into thethickness t (300) of the tissue 276 at the point of the incidence of theultrasound pulse 290. As the catheter housing 16 is traversed in amanner 301 across the tissue 276, the sensor 40 detects the gap distanced (282), lesion characteristics, and the tissue thickness t (300). Thesensor preferably detects these parameters continuously, but mayalternatively detect them periodically or in any other suitable fashion.This information is used in delivering continuous ablation of the tissue276 during therapy as discussed below.

The Processor. The energy delivery system 10 of the preferredembodiments also includes a processor, coupled to the sensor 40 and tothe electrical attachment 14, that controls the electrical pulsedelivered to the electrical attachment 14 and may modify the electricalpulse delivered based on the information from the sensor 40. Theprocessor is preferably a conventional processor or logic machine thatcan execute computer programs including a microprocessor or integratedcircuit, but may alternatively be any suitable device to perform thedesired functions.

The processor preferably receives information from the sensor such asinformation related to the gap distance, the thickness of the tissuetargeted for ablation, the characteristics of the ablated tissue, andany other suitable parameter or characteristic. Based on thisinformation, the processor converts this information into a gapdistance, a thickness of the tissue targeted for ablation, acharacteristic of the ablated tissue, and any other suitable parameteror characteristic and/or controls the energy beam 20 emitted from theenergy source 12 by modifying the electrical pulse sent to the energysource 12 via the electrical attachment 14 such as the frequency, thevoltage, the duty cycle, the length of the pulse, and/or any othersuitable parameter. The processor preferably also controls the energybeam 20 by controlling which portions of the energy source 12 areenergized and/or at which frequency, voltage, duty cycle, etc. differentportions of the energy source 12 are energized. Additionally, theprocessor may further be coupled to a fluid flow controller. Theprocessor preferably controls the fluid flow controller to increase ordecrease fluid flow based on the sensor detecting characteristics of theablated tissue, of the unablated or target tissue, and/or any othersuitable condition.

By controlling the energy beam 20 (and/or the cooling of the targetedtissue), the shape of the ablation zone 278 is controlled. For example,the depth 288 of the ablation zone is preferably controlled such that atransmural (through the thickness of the tissue) lesion is achieved.Additionally, the processor preferably functions to minimize thepossibility of creating a lesion beyond the targeted tissue, forexample, beyond the outer atrial wall. If the sensor detects the lesionextending beyond the outer wall of the atrium or that the depth of thelesion has reached or exceeded a preset depth, the processor preferablyturns off the generator and/or ceases to send electrical pulses to theelectrical attachment(s) 14. Additionally, if the sensor detects, forexample, that the system 10 is not centered with respect to thepulmonary vein PV by detecting the distance of the target tissue withrespect to the energy source and/or intended ablation path, theprocessor may either turn off the generator and/or cease to sendelectrical pulses to the electrical attachment(s) 14, may alter thepulses sent to the electrical attachment, and/or may alter the operatoror motor drive unit to reposition the system with respect to the targettissue.

Additional Elements. As shown in FIG. 1, the energy delivery system 10of the preferred embodiments may also include an elongate member 18,coupled to the energy source 12. The elongate member 18 is preferably acatheter made of a flexible multi-lumen tube, but may alternatively be acannula, tube or any other suitable elongate structure having one ormore lumens. The elongate member 18 of the preferred embodimentsfunctions to accommodate pull wires, fluids, gases, energy deliverystructures, electrical connections, therapy catheters, navigationcatheters, pacing catheters, and/or any other suitable device orelement. As shown in FIG. 1, the elongate member 18 preferably includesa housing 16 positioned at a distal portion of the elongate member 18that functions to enclose the energy source 12 and the reflectionsurface 100. The elongate member 18 further functions to move andposition the energy source 12 and/or the housing 16 within a patient,such that the emitted energy beam 20 contacts the target tissue at anappropriate angle and the energy source 12 and/or the housing 16 ismoved along an ablation path such that the energy source 12 provides apartial or complete zone of ablation along the ablation path.

The energy delivery system 10 of the preferred embodiments may alsoinclude a lens or mirror, operably coupled to the energy source 12, thatfunctions to provide additional flexibility in adjusting the beampattern of the energy beam 20. The lens is preferably a standardacoustic lens, but may alternatively be any suitable lens to adjust theenergy beam 20 in any suitable fashion. The lens may be used to focus ordefocus the energy beam. For example, an acoustic lens could create abeam that is more uniformly collimated, such that the minimum beam widthD.sub.1 approaches the diameter D of the energy source 12. This willprovide a more uniform energy density in the ablation window, andtherefore more uniform lesions as the tissue depth varies within thewindow. A lens could also be used to move the position of the minimumbeam width D.sub.1, for those applications that may need eithershallower or deeper lesion. This lens could be fabricated from plasticor other material with the appropriate acoustic properties, and bondedto the face of energy source 12. Alternatively, the energy source 12itself may have a geometry such that it functions as a lens, or thematching layer or coating of the energy source 12 may function as alens.

Although omitted for conciseness, the preferred embodiments includeevery combination and permutation of the various energy sources 12,electrical attachments 14, energy beams 20, sensors 40, and processors.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claim, modifications and changescan be made to the preferred embodiments of the invention withoutdeparting from the scope of this invention defined in the followingclaims.

What is claimed is:
 1. A system for ablating tissue, said systemcomprising: an elongate shaft having a proximal portion, a movabledistal portion, and a longitudinal axis; and an ablation elementcomprising an ultrasound transducer disposed within a housing, thehousing coupled to the movable distal portion of the elongate shaft,wherein the ultrasound transducer comprises a single ultrasoundtransducer element having an active portion and an inactive portion,wherein the ultrasound transducer is configured to sense a distancebetween the ultrasound transducer and a target tissue or to senseproperties of the target tissue, wherein the housing comprises an openwindow, and wherein the ultrasound transducer is configured to deliver acollimated beam of ultrasound energy comprising ablation energy to thetarget tissue through the open window without contacting a zone ofablation with the elongate shaft or any structure disposed thereon,thereby ablating at least a portion of the target tissue.
 2. The systemof claim 1, further comprising a reflecting element operably coupledwith the ultrasound transducer, the reflecting element redirecting thebeam of ultrasound energy emitted from the ultrasound transducer tochange a direction or a pattern of the beam of ultrasound energy.
 3. Thesystem of claim 2, wherein the reflecting element is non-expandable. 4.The system of claim 2, wherein the reflecting element is configured tomove relative to the ultrasound transducer so that the beam ofultrasound energy is emitted at varying angles or positions.
 5. Thesystem of claim 2, wherein the reflecting element is disposed within thehousing.
 6. The system of claim 1, wherein the properties of the targettissue comprise target tissue thickness or properties of the ablatedtarget tissue.
 7. The system of claim 1, wherein the system isconfigured to direct the ultrasound beam along a path such that the zoneof ablation has a ring shape, elliptical shape, linear shape,curvilinear shape, or combinations thereof.
 8. The system of claim 1,wherein the housing is non-expandable and non-reflective.
 9. The systemof claim 1, wherein the properties of the target tissue comprise targettissue thickness or depth of the zone of ablation.
 10. The system ofclaim 1, wherein the ultrasound transducer is configured to sense adistance between the ultrasound transducer and the target tissue and tosense properties of the target tissue.
 11. The system of claim 1,further comprising a processor configured to adjust the beam ofultrasound energy in response to the sensed distance or the sensedproperties of the target tissue.
 12. The system of claim 11, wherein theprocessor is configured to adjust one or more of a frequency, a voltage,a duty cycle, a pulse length, or a position of the beam of ultrasoundenergy in response to the sensed distance or the sensed properties ofthe target tissue.
 13. The system of claim 1, further comprising abacking layer coupled to the ultrasound transducer, the backing layerconfigured to provide a heat sink for the ultrasound transducer.
 14. Thesystem of claim 13, wherein the backing comprises a plurality of groovesextending longitudinally along an outside wall of the backing.
 15. Thesystem of claim 1, wherein the inactive portion comprises a materialconfigured to conduct heat away from the active portion.
 16. The systemof claim 1, further comprising a flow of fluid configured to cool theultrasound transducer.
 17. The system of claim 1, wherein the beam ofultrasound energy is emitted from the ablation element in a directionrelatively aligned with the longitudinal axis of the elongate shaft andwherein the beam of ultrasound energy is emitted from the housing in adirection relatively transverse to the longitudinal axis of the elongateshaft and the beam of ultrasound energy forms a zone of ablationcomprising a continuous lesion in the target tissue.
 18. The system ofclaim 1, wherein, during ablation of the portion of the target tissue,the housing is configured to shield the ablation element from blood. 19.A method for ablating tissue, said method comprising: providing anablation system comprising an elongate shaft and an ablation element,the ablation element comprising an ultrasound transducer disposed withina housing coupled to a distal portion of the elongate shaft, wherein thehousing comprises an open window, wherein the ultrasound transducercomprises a single ultrasound transducer element having an activeportion and an inactive portion; positioning the ablation elementadjacent a target tissue; delivering a collimated beam of ultrasoundenergy comprising ablation energy from the ultrasound transducer to thetarget tissue through the open window without contacting a zone ofablation with the elongate shaft or any structure disposed thereon;sensing a distance between the ultrasound transducer and the targettissue with the ultrasound transducer, or sensing properties of thetarget tissue with the ultrasound transducer, and ablating at least aportion of the target tissue with the beam of ultrasound energycomprising the ablation energy, thereby forming the zone of ablationcomprising a continuous lesion in the target tissue.
 20. The method ofclaim 19, wherein delivering the beam of ultrasound energy comprisesreflecting the beam of ultrasound energy off of a reflecting elementoperably coupled with the ultrasound transducer thereby redirecting thebeam of ultrasound energy and changing a direction or pattern of thebeam of ultrasound energy.
 21. The method of claim 20, whereinreflecting the beam of ultrasound energy comprises moving the reflectingelement relative to the ultrasound transducer so that the beam ofultrasound energy is emitted at varying angles or positions.
 22. Themethod of claim 19, wherein the lesion is a ring shape, ellipticalshape, linear shape, curvilinear shape, or combinations thereof.
 23. Asystem for ablating tissue, said system comprising: an elongate shafthaving a proximal portion, a movable distal portion, and a longitudinalaxis; an ablation element comprising an ultrasound transducer disposedwithin a housing, the housing coupled to the movable distal portion ofthe elongate shaft, wherein the ultrasound transducer comprises a singleultrasound transducer element having an active portion and an inactiveportion, wherein the ultrasound transducer is configured to sense adistance between the ultrasound transducer and a target tissue, or tosense properties of the target tissue, wherein the ultrasound transduceris configured to deliver a collimated beam of ultrasound energycomprising ablation energy to the target tissue without contacting azone of ablation with the elongate shaft or any structure thereon,thereby ablating at least a portion of the target tissue.
 24. A methodfor ablating tissue, said method comprising: providing an elongate shaftand an ablation element, the ablation element comprising an ultrasoundtransducer disposed within a housing coupled to a distal portion of theelongate shaft, wherein the ultrasound transducer comprises a singleultrasound transducer element having an active portion and an inactiveportion; positioning the ablation element adjacent a target tissue;delivering a collimated beam of ultrasound energy comprising ablationenergy from the ultrasound transducer to the target tissue withoutcontacting a zone of ablation with the elongate shaft or any structuredisposed thereon; sensing a distance between the ultrasound transducerand the target tissue with the ultrasound transducer; and or sensingproperties of the target tissue with the ultrasound transducer ablatingat least a portion of the target tissue with the beam of ultrasoundenergy comprising the ablation energy, thereby forming the zone ofablation comprising a continuous lesion in the target tissue.